1. Technical Field
The subject invention relates to a novel mammalian antiproliferative protein, prohibitin, and uses thereof. For example, prohibitin may be utilized in the treatment of diseases involving excess cellular replication, such as cancer, or in the treatment of conditions involving an insufficient amount of cellular replication, such as impaired tissue regeneration.
2. Background Information
The ability to negatively regulate cell proliferation is a necessity for all living organisms. Unicellular organisms must limit their replication to the time when adequate nutrients and other environmental factors are present, and multicellular organisms must accurately shape and maintain the architecture of their component tissues. The failure in a multicellular organism to provide adequate negative growth control in the developmental period may result in a malformation, which may be lethal. In the postdevelopmental period, such a failure may result in neoplasia. Because negative control is so critical, specific genes have evolved whose role is actively antiproliferative.
Tumor suppressor genes are a class of genes that have been identified based on an association between neoplasia and the loss of function in both copies of the gene (Klein, G., Science 238:1539-45 (1987); Hansen et al., Cell 53:172-73 (1988); Ponder, B., Nature 335:400-02 (1988); Sager, R., Science 246:1406-12 (1989)). While the existence of more than ten tumor suppressor genes is predicted based on such associations, only four such genes have been cloned to date: (1) retinoblastoma (Friend et al., Nature 323:643-46 (1986); Lee et al., Nature 329:642-45 (1987); Fung et al., Science 236:1657-61 (1987)), (2) p53 (Oren et al., Proc. Natl. Acad. Sci. USA 80:56-59 (1983)), (3) Wilms' tumors (Call et al., Cell 60:509-20 (1990); Rose et al., Cell 60:495-508 (1990); Gessler et al., Nature 343:774-78 (1990)) and (4) dcc (Fearon et al., Science 247:49-56 (1990). The retinoblastoma gene product and p53 appear to be nuclear proteins (Lee et al., Science 235:1394-99 (1987); Rotter et al., J. Virol. 36:547-55 (1980); Dippold et al., Proc. Natl. Acad. Sci. USA 3:1695-99 (1981)). The Wilms' tumor gene product has a structure similar to that of other transcription factors (Call et al., supra; Gessler et al., supra). The dcc gene product resembles neural cell adhesion molecules (Fearon et al., supra).
Tumor suppressor genes may be only a subset of the important negative regulatory genes in the cell. A hypothetical second class of negative regulators would be antiproliferative genes whose loss of function kills the cell. A lethal outcome might occur for any number of reasons, such as when internal growth signals become too great for the maintenance of homeostasis.
In general, negative growth control genes that act within mammalian cells have been extremely difficult to isolate. Despite intensive research in recent years, only a small number of genes have been cloned for whom such an activity is likely. Of this subset, only four genes have been shown to be directly antiproliferative by expressing them in cells in tissue culture: the retinoblastoma gene product (Huang et al., Science 242:1563-66 (1988)), p53 (Mercer et al., Proc. Nat'l Acad. Sci. USA 87:6166-70 (1990), a ras-related transformation suppressor gene (Kitayama et al., Cell 56:77-84 (1989), and prohibitin (McClung et al., Biochem. Biophys. Res. Commun. 164:1316-22 (Nov. 15, 1989)).
The first cDNA for prohibitin was isolated using a different strategy than that used to isolate tumor suppressor genes (McClung et al., Supra). This cDNA was originally identified as one of a set of cDNAs corresponding to mRNAs more highly expressed in normal than in regenerating liver. It was then shown that prohibitin mRNA, enriched by hybrid selection, could block DNA synthesis when microinjected into normal fibroblasts. No match was found between the partial cDNA clone and sequences in the GenBank database.
All U.S. patents and publications referred to herein are hereby incorporated by reference.